Power MOSFET devices are commonly used in electronic circuits. Depending on the application, different device characteristics may be desirable. One example application is a DC-DC converter. Schottky diodes are often employed as rectifiers in DC-DC converters and in numerous other power and small signal applications where the forward conduction or switching characteristics of the diode are important. These diodes are used extensively as output rectifiers in switching-mode power supplies and in other high-speed power switching applications such as motor drives for carrying large forward currents. Ultra-low forward voltage drop (Vf) under conduction and relatively good blocking performance under a reverse bias, as well as fast reverse recovery time are the desirable characteristics of an efficient Schottky diode.
A Schottky diode is desired that can be monolithically integrated with MOSFET devices in the active region contact trench. The Schottky diodes (SKY) reduce the body diode forward voltage drop (Vf) and minimize the stored charge, and have a quick reverse recovery time, making the MOSFET more efficient. The leakage current drain to source (Idss) of the Schottky diode is related to the Schottky barrier height. As the barrier height increases, the leakage current decreases, and the forward voltage drop also increases.
For trench MOSFET devices with an integrated Schottky diode formed on flat surface or on large trench contact surface, the Schottky diode is formed without a Tungsten (W) plug. In a trench MOSFET device with a high aspect ratio, e.g., 2.5:1 or greater, the trench contact critical dimension (CD) is very small (i.e., about 0.35 micron width), and tungsten plugs are used in order to form good ohmic contact and avoid forming a contact void.
It is within this context that embodiments of the present invention arise.